The present disclosure relates to a communication system and a communication apparatus which includes an interrogator transmitting an interrogation signal and responders returning a response signal in response to the interrogation signal, and more particularly, to a communication system and a communication apparatus which includes one interrogator and a plurality of responders and in which the interrogator sequentially communicates with the respective responders while preventing a collision error.
A communication system such as RFID includes an interrogator transmitting an interrogation signal and a responder returning a response signal in response to the interrogation signal. Many kinds of communication systems perform non-contact communication or proximity communication. The responder has the features of low power consumption and low cost to obtain driving power from the interrogation signal. In general, since the communication system includes one interrogator and a plurality of responders, it is desirable that the interrogator efficiently communicates with the plurality of responders.
For example, when a unique identification code and a random code having a hierarchical structure are written into an IC tag and no search can be performed due to collision of the random code of Layer zero, the search is performed with the random code of Layer one. There has been suggested a communication method of accelerating search of an IC card by performing search in each layer (for example, see Japanese Unexamined Patent Application Publication No. 2000-131423).
Moreover, there has been suggested a system in which a responder changes a transmission timing at random, returns an operation response signal, stores identification codes included in the operation response signal received by an interrogator in a predetermined sequence, stops communication for a predetermined period when communication normally ends, correctly recognizes all of the plurality of unspecified responders, and reduces a probability that the operation response signals of the responders collide with each other (for example, see Japanese Unexamined Patent Application Publication No. 6-201821).
Furthermore, there has been suggested a communication method in which the unique identification codes of the respective responders are stored, an interrogator transmits a data request signal attached with the identification code of a responder with which the interrogator desires to communicate, and only the responder having the own identification code matching with the identification code responds to the data request signal (for example, Japanese Unexamined Patent Application Publication No. 63-5286, Japanese Unexamined Patent Application Publication No. 1-314985, and U.S. Pat. No. 5,434,572).
In a communication system including one interrogator and a plurality of responders, there is a concern that a collision error occurs when the interrogator simultaneously receives responses from the plurality of responders. When the collision error occurs, the interrogator has to transmit the interrogation signal again and give a request for supplying information to the responders. However, a problem may arise in that communication efficiency may deteriorate and the interrogator may not acquire necessary information from the responders.
Moreover, the responders have to be in a standby state to respond to the interrogation signal from the interrogator. The responders consume power when the responders are in the standby state. Therefore, the responders may become a cause of heat generation or a noise source for the other responders. When the responder is equipped with a measurement mechanism such as a temperature sensor, correct sensor information may not be acquired due to the heat or noise generated from the responder.
When the interrogator is configured to transmit an interrogation signal designated for an individual responder, the collision error may be prevented. In this case, however, the responder has to include the function of a reception circuit to understand an interrogation from the interrogator (perform decoding). For this reason, the size of the responder may be increased, and thus an increase in power consumption and high cost may be caused.